Criticality in the planform behavior of the Ganges River meanders

The critical point of planform transition from straight to meandering in the wandering Ganges River is identifiable. Recent remote-sensing data indicate that four similar meanders cut off, or attempted to cut off, after approximately 31-35 yr, primarily due to channel aggradation. As main channels aggrade, sinuosity is maximized for broad channel widths and small radii of curvature and relaxes for bends of greater radii. Maximized form resistance occurs close to self-organized criticality and promotes cutoffs. Avulsions lead to main channel narrowing and prevent further bend tightening, relaxing the system by reducing sinuosity. Thus, the wandering river oscillates in space and time across the transition from a more ordered to a more chaotic state. Planform behavior is described by the Jerolmack-Mohrig mobility number and the Parker stability criterion, which well define meanders behavior as they approach criticality and then relax via partial or completed avulsions. The results have significance for river engineering and river network and stratigraphic modeling. Such an approach could be of practical value when predicting the behaviors of other major wandering rivers.